1. Field of the Invention
The present invention relates to new and useful improvements in semi-permeable membrane separation equipment for an ultrafiltration system, and more particularly to such an equipment in which casings for receiving ultrafiltration membrane cartridges are provided as separate units with respect to a vertical casing which receives a submerged axial-flow pump, so as to be radially arranged around the outside of the vertical casing so that the equipment has a star-like shape in its plan view.
2. Description of the Prior Art
As described in U.S. Pat. Nos. 3,893,920 and 3,984,319, in a conventional type of an ultrafiltration system hitherto employed widely, a plurality of ultrafiltration membrane cartridges are detachably mounted on an inner surface of each of the sidewalls of a single canister which has a large-sized common casing having a square shape in transverse cross-section. In such a conventional system, as shown in FIGS. 6 and 7 of the accompanying drawings, a plurality of ultrafiltration membrane cartridges 50 one unit of which is shown in FIG. 5 are mounted on the inner surface of each of the sidewalls 4a of a large-sized outer casing 4 having a square shape in transverse cross-section, so as to form four adjacent columns as shown in FIG. 7, each of which columns consists of three stacked units as shown in FIG. 6. In a central portion of the interior of the outer casing 4, there is provided a vertical pump casing 2 having both of its upper and lower end portions open, in which pump casing 2 an axial-flow pump 1 comprising an impeller 3 is disposed. The pump 1 is driven by a drive means or drive motor 7 which is provided in either an upper portion or a lower portion of the outer casing 4 so as to feed carrier water into the ultrafiltration membrane cartridges 50. Incidentally, the reference numeral 6 designates a frame for supporting the casing 4.
As described above, when the drive means for the impellar 3 of the axial-flow pump 1 is installed in the upper portion of the outer casing 4 of the conventional ultrafiltration system, there is a problem in the case of installation in a basement with restricted height, because the overall height of the system is too great. On the other hand, when the drive means is installed in the lower portion of the casing 4, the drive means is disposed outside the casing 4 in a horizontally projecting manner so as to increase the floor space required beyond that of the main casing 4. In addition such an arrangement of the drive means in the lower portion of the casing 4 is less effective in reducing the overall height of the system because of the necessity of providing a bearing mechanism for the impeller 3, which bearing mechanism must be provided in a lower portion of the vertical pump casing 2.
A conventional ultrafiltration system having the above construction is also disadvantageous in that the installation and maintenance of such drive means are difficult, and a further disadvantage arises from the noise and vibrations caused during operation in both the upper and lower flow regions of the main casing 4, in which regions the flow path for the incoming water is changed from a square to a circle or vice versa in transverse cross-section creating a turbulent flow which generates such noise and vibrations.
In addition, the conventional ultrafiltration system also has the following problems which affect the system's perfomance. In the conventional system, since it is not possible sufficiently to increase the height of the main casing 4 which receives the ultrafiltration membrane cartridges 50 due to the installation of the drive means, it is substantially not possible to stack the cartriges more than three units high. Consequently, in order to achieve a required perfomance level, it is necessary to increase the number of adjacent columns of the stacked cartridges 50. However, such an increase in the number of the adjacent columns requires an increased width of the sidewall 4a of the casing 4, which leads to a larger overall size of the system making it impossible to reduce the size of the system. For the above reasons, the conventional system employs an arrangement of the cartridges 50 in four adjacent columns at each side each of which columns contains three stacked units as shown in FIGS. 6 and 7, and still suffers from much difficulty in transportation and installation of the system due to its large size. The conventional system is further disadvantageous in that there is wasted space in the region in which the ultrafiltration membrane cartridges 50 are mounted on the inner surface of each of the sidewalls 4a of main casing 4. Further, as described above, since the conventional system has a relatively large number of columns of stacked cartridges 50 mounted on the inner surface of each of the sidewalls 4a of the casing 4, the cross-sectional area of the flow path of the raw water passing through the cartridges 50 is large resulting in high power consumption. This is yet another disadvantage inherent in the conventional system.